Paper testing method



March 4, 1958 J. CONNELL ETAL I 2925,25

PAPER TESTING METHOD Filed Aug. 11, 1955 INVENTOR J 5i. 0mm

06 0b. R g/wni BYFZM'AL/ JwAWNfi Pan/km ATTORNEYS 3 2,825,225 lcfi l atented Mar. 4, 19.58

PAPER TESTING METHOD Herbert J. Connell, Cape Elizabeth, and Clyde P. Grant, Gorham, Maine, assignors to S. D. Warren Company, Boston, Mass., a corporation of Massachusetts Application August 11, 1955, Serial Na. 527,829 2 Claims. (c1. 73-159 Paper has a variety of specific defects which cause United States Patent() difficulties when the paper is used for printing. The defects with which the present invention is concerned are due to the presence on the surface of the paper of more or less readily removable particles or dust. Some of these defects are known in the trade by the following names: haze, fiber,pickouts, coating lumps and surface dirt. Haze may be described as loosely bound material on the surface of the paper which separates from the paper during printing, especially in offset printing and appears as a whitish deposit on the offset press blanket. This deposit makes it necessary to wash up the printing press more or less frequently depending upon the amount of the haze. Fiber is loosely bound fibrous material which comes from the paper base and gives rise to the same difficulties in printing as does haze. Pickouts result from weak areasin the paper surface. In printing, the material in such weak areas is picked out and deposited on different parts of the printing press. It sticks to the plate in letterpress printing and to the blanket in offset printing and may cause subsequent pickouts, called repeats, due to increased impression. Coating lumps are inadequately dispersed pigment agglomerates which are inadequately bound in the paper surface. In printing these lumps may break and liberate material which deposits on, the plate or blanket making cleanup necessary.

An object of the present invention is to provide a method of determining the presenceand degree of such defects in paper i. e. defects which may result in the separation of fine particles or dust from the paper surface and give rise to defects or difficulties in printing.

A further object of our invention is to provide a method of testing the paper on the paper machine without interrupting its continuous operation because the defects are first observable on the paper machine and because steps may be taken to correct the defects by adjustment of the operation of the paper machine. Moreover by testing the paper for defects on the paper machine the production of a large amount of defective paper may be avoided i. e. a defect may be detected as soon as or shortly after it first appears and steps may be taken immediately to correct it.

The testing method comprisesthe steps of applying a clean roller having a black surface capable of picking the dust off of the paper as it travels in the paper machine, applying a strip of pressure sensitive adhesive tape such as Scotch tape to the roller and then stripping it off and comparing the area from which the adhesive tape has been stripped with the remainder of the area of the roller to observe the difference in color. A series of standards may be set up so that the paper tested may be given a rating. For instance the paper might be rated as being free, trace, light, moderate or heavy or numbers or letters might be used to indicate different degrees of defectiveness of the paper surface as indicated by the roller test. These different degrees of defectivenesscan of course be correlated to the relative utility of the paper for printing. For instance a particular customer or a particular printing process may require a paper which shows no more than a trace of haze according to a predetermined series of standards.

A device which is suitable for carrying out the method consists of a black or dark colored rubber roller mounted on a shaft having a handle by means of which the roller may be pressed against the paper. The size of the roller may vary within a rather wide range but we have found a roller of the following dimensions to be satisfactory.

The rubber of the roller surface must be sufficiently tacky to pick up and retain the dust from the paper surface. Rubber rollers supplied by manufacturers to users for various purposes generally are rated according to the density or hardness of the rubber. Several standards of density or hardness are described in the literature. These standards are all based upon the degree of penetration of the rubber by a ball or pin of a specified size and shape under a specified pressure. Three such standards are known as plastometer, densimeter and durometer. We have found that a roller made of rubber having a durometer value of about 50 or a plastometer value of about gives satisfactory results. Considerable variation from these values are permissible but as is apparent the roller surface must not be so hard that it will not pick up dust or so tacky and adhesive that it will pull away any integral part of the paper. We have further found that a roller having a suitably tacky surface shows a coefficient of static friction on a clean glass surface of 2.42. A further method of determining an operable tackiness of the rubber of the roller is to use a roller having substantially the same hardness and tackiness as the rubber of the blanket of the offset printing press on which the paper is to be printed because the purpose of the test is to determine the amount of such dust on the paper that will adhere to said blanket. The rubber roller must of course not be so tacky that it will not transfer the dust taken off of the paper to the adhesive tape. The roller must of course be a substantially true cylinder and must have a smooth, even surface.

An illustrative embodiment of the device described above is shown in the accompanying drawings in which Fig. l is a perspective view of the clean roller and its 7 supporting shaft, frame and handle Fig. 2 is a front elevational view of the roller after it has been applied to paper to be tested and a strip of adhesive tape has been applied and Fig. 3 is a front elevational view of the roller after the adhesive tape has been removed.

Referring to the drawings 1 is the roller, 2 is the U- shaped frame which supports the roller shaft 3 and 4 is the handle.

As appears in Fig. 2 the roller is covered with a layer of dust as a result of contact with paper having this defect. As appears from Figs. 2 and 3 the strip of adhe- .sive tape 5, after being firmly pressed against the roller with 'water and soap or other detergent or washing it with one of the well known rubber cleaning solvents or by applying a pressure sensitive adhesive tape to the entire surface of the roller and stripping it ofi. The dry clean roller is held 'in contact with the paper travelling in the paper machine for instance at the windup reel. The amount of pressure applied is not critical so long as the roller makes good contact with the paper. Ordinarily the weight of the roller is sufficient and additional pressure need not be applied. The roller should be held in contact with the paper while it traverses a standard length thereof if the results of different tests are to be comparable. We have found that 20 seconds of contact with paper traveling at the rate of 500 feet per minute usually is suflicient. Thus each point on the roller will be brought into contact with the paper about 160 times. It is obvious however that a different standard may be set and may be expedient. After contact with the paper a strip of adhesive tape is applied to the roller as shown in Fig. 2, pressed down firmly and then stripped off and the color of the stripped area compared with the color of the remainder of the surface of the roller.

As is obvious either the roller or the paper or both rolling a roller having a tacky surface in contact with the surface of the paper, applying a strip of pressure sensitive adhesive tape to a portion of the surface of the roller, stripping the tape from the roller and comparing the color of the stripped off area of the roller with that of the adjacent surface of the roller.

2. Method of testing paper for dust which comprises bringing a roller having a tacky surface into contact with a moving paper Web at a fixed location, the axis of said roller being parallel to the paper web and perpendicular to the direction of movement thereof whereby said roller is caused to rotate with said tacky surface in contact with said paper web, maintaining said roller in contact with said paper web until a predetermined length of said paper web has moved in contact with said roller, separating said roller from said paper web, cleaning a portion only of said tacky surface and comparing the resulting cleaned area with an adjacent uncleaned area.

References Cited in the file of this patent UNITED STATES PATENTS 2,624,060 McKenzie Ian. 6, 1953 2,705,424 Pomper Apr. 5, 1955 FOREIGN PATENTS 632;020 Germany June 11, 1936 

